Yes, it's the lightbulb moment I was writing about in my last post! I actually can't believe it happened almost on request.
The problem was that my characters weren't behaving themselves, or rather, I felt I was losing a sense of them as characters. What resulted was a bland, tensionless disaster of a chapter. My friend/critique partner pointed this out, and though it was painful to admit there was a lot wrong with the chapter, I sucked it up and made changes.
What needed to happen wasn't obvious at first. I let her comments simmer in my head, and it didn't actually take that long for the ideas to start germinating.
My lightbulb moment was that I hadn't lost my characters, but rather, that the chapter wasn't working because their actions were OUT of character. Once I figured out the natural thing for them to do, I could hear the story's engine revving once more. All sorts of possibilities grew out of the one change I made to the chapter. Now I have options. Before the realisation, the story was laying flat and stagnant, with hardly a sign of life.
I have re-written the chapter and received the tick of approval from AbFab. Right now, I'm at the start of chapter 7, right smack in the middle of the novel. The characters are doing what comes naturally and it's given me a believable 'Point Of No Return', which in the previous version (the dud chapter) was nowhere in sight.